Initialize wide struct info.

Fixes 15381.

Using wide character function is on byte oriented memstream is undefined
behaviour.  This behaviour was masked by not initializing wide struct
info. We now initialize it to cause a predictable crash.

libio/genops.c

@@ -661,6 +661,10 @@ _IO_no_init (fp, flags, orientation, wd, jmp)
 
       fp->_wide_data->_wide_vtable = jmp;
     }
+  else
+    /* Cause predictable crash when a wide function is called on a byte
+       stream.  */
+    fp->_wide_data = (struct _IO_wide_data *) -1L;
 #endif
   fp->_freeres_list = NULL;
 }